1. Technical Field
The present invention relates to a disk drive and an information processing system having the disk drive, and more particularly to control of the number of rotations of a disk.
2. Related Art
Techniques for controlling the number of rotations of a disk to an optimum number of rotations have hitherto been proposed. For instance, JP2004-362733A describes a technique for comparing a cache activity ratio with two threshold values; namely, a high threshold value and a low threshold value, and controlling the number of rotations of a disk in accordance with results of comparison. Further, controlling the number of rotations in accordance with a command interval is also disclosed.
JP 2002-8316 A describes a technique for measuring an average transfer rate of data transferred from cache memory to a host; comparing the thus-measured average transfer rate with a threshold value; and controlling the number of rotations of a disk in accordance with a result of comparison.
JP 2007-48366 A describes a technique for increasing the rotational speed of a motor that rotates a disk when a transfer rate of data to be written/read exceeds a threshold value Rth and when a duration of time, in which the transfer rate exceeds the threshold value Rth, continues a threshold value Tth or more and decreasing the rotational speed of the motor that rotates the disk when a transfer rate of data to be written/read falls below the threshold value Rth and when a duration of time, in which the transfer rate falls below the threshold value Rth, continues the threshold value Tth or more.
JP 2006-147119 A describes a technique for identifying whether current operation is audio playback or ripping (capturing data from a CD or a DVD directly and into a personal computer or converting the data into an image file or another file format and capturing the thus-converted data into the personal computer) in accordance with the configuration of a command pattern issued without measurement of a transfer rate and determining the rotational speed of a disk.
JP 2000-132901 A describes a technique for controlling rotational speed in accordance with a file size.
Moreover, JP 2003-242711 A describes a technique for controlling the rotational speed of a disk in accordance with an idle time of a drive (a time elapsing from when execution of a command is completed until when performance of the next command is commenced).
Controlling the rotational speed of a disk in an incrementing or decrementing manner in accordance with the activity ratio of cache memory or the transfer rate of data is effective. However, drive load exerted on a motor changes from the case of an increase in rotational speed of a disk and the case of a decrease in rotational speed. Hence, control must be performed in consideration of this point. Moreover, cache memory is originally intended for enhancing a data read rate by increasing a hit rate, and hence nature of a command must be taken into account.